Mary Riddell is a columnist and a political interviewer for the Daily Telegraph. She writes on topics ranging from family to foreign policy and is particularly interested in criminal justice. Her focus is what is going on, for better or for worse, in the Parliamentary Labour Party.

Whether McCluskey is the sort of enemy that Miliband needs is, at first sight, questionable. Not only are the unions the paymasters of Labour. In addition, his intervention appears to leave Miliband marooned between the Left of his party and the Blairite Right, who, as McCluskey warns, may sense their power returning and be tempted one day to turn on Miliband.

Alienating McCluskey was inevitable. The cause of his fury is the speech Ed Balls gave on Saturday, endorsing the public sector pay freeze and saying that he could not promise to reverse any Coalition cuts. Balls did not, as McCluskey suggests, sign up to austerity on the spur of the moment. He had been considering his shift for a year and spoke when he judged the moment to be right.

It is likely that both he and Miliband knew exactly what union reaction he might provoke and even hoped that things would work out as they have. For sure, money is a problem. Labour has been in hock to the unions for too long, and may soon be forced to think radically about future funding. But Miliband is also vulnerable to the charge that he, a fighter against vested interests, is in the grip of one of the most powerful forces around.

If he can stand up to McCluskey, it will do his flagging reputation no harm at all. He must gamble that, while teachers, health workers and public servants who are seeing their relatively meagre wages decline will be furious, when it comes to an election, many will feel that they have nowhere else to go. In the meantime, they might even buy the Balls argument that the focus must be on the jobless.

As for McCluskey, he may also have no option but to reach a compact with Miliband and Balls. It is not as if there is a hard Left Labour princeling waiting in the wings. For the unions, the two Eds are as good as it gets. For the public, it is vital that Labour establish itself as a party of courage and economic credibility.